1. Field of Invention
The present invention relates, in general, to retractable writing instruments and, more particularly, to a screw-type writing instrument having an expansion and contraction function which is portable and serves as a fashion accessory.
2. Background
Generally, a retractable writing instrument has a pen core advancing and retracting mechanism such that the tip of the pen core, which is provided in the casing of the writing instrument, can be advanced when one desires to write something, and can be retracted when not in use. This mechanism may be applied to a ballpoint pen, a mechanical pencil, a multi pen, etc.
In the case of a writing instrument having no pen core advancing and retracting mechanism, because the writing instrument can have a small size thanks to the reduced axial length thereof, it may be used as a decorative article, a character product or a fashion accessory as well as having its inherent function as a writing instrument. However, the writing instrument having no pen core advancing and retracting mechanism requires a separate covering means, such as a lid, which eliminates a safety hazard, protects the pen tip, and prevents cloth from becoming stained with ink. This writing instrument is inconvenient because a user must open the separate lid every time he/she desires to use it. Furthermore, there is a disadvantage in that the lifetime of the writing instrument is reduced if the lid is lost.
Meanwhile, in the case of a writing instrument having a pen core advancing and retracting mechanism, because the length of the pen core advancing and retracting mechanism is added to the length of the pen core, the overall length of the writing instrument is longer than that of the writing instrument having no pen core advancing and retracting mechanism. Therefore, in this case, the writing instrument is not suitable for use as a decorative article or a character product and is relatively inconvenient to hold and carry.
In an effort to overcome the above-mentioned problems, a pen tip advancing and retracting device of a writing instrument having an expansion and contraction function was proposed in Korean Utility Model Registration No. 0038481, which was filed in 1988. In this technique, a main body and a cap body are coupled to each other and expand and contract in length. A member, which is integrated with a protective tube coupled to an ink tube, is mounted to the upper end of the main body. A longitudinal hole is formed at a predetermined position in the member, so that the upper end of a pin having a predetermined length is inserted into the longitudinal hole of the member. Here, a protrusion is provided at a predetermined position on the pin, and the pin further extends a length from the protrusion sufficient for the pin to be inserted upwards into the longitudinal hole. Furthermore, one end of the pin is enlarged in diameter. A bushing having a flange is inserted into the lower end of the protecting tube, and a typical coil spring and a conical cap are provided outside the bushing and are screwed to the outer surface of the lower end of the main body. Then, the flange, to which the elasticity of the coil spring is applied, is brought into contact with the lower end of the pin. Meanwhile, a head member is fastened to the cap body such that the upper end of the pin is in close contact with the bottom of the head member.
However, in the conventional pen tip advancing and retracting device of the writing instrument, a large number of elements is required to achieve the purpose of the conventional technique, that is, 1) the main body, 2) the cap body, 3) the ink tube, 4) the protecting tube, 5) the member, 6) the pin, 7) the bushing, 8) the coil spring, 9) the conical cap and 10) the head member. Therefore, the conventional technique has disadvantages of reduced productivity and manufacturability.
Furthermore, the conventional pen tip advancing and retracting device of the writing instrument has a mechanism in which a pen tip is advanced by contacting the bottom of the head member with the upper end of the pin, and is retracted by the elasticity of the coil spring in a second stage after the expansion or contraction process has been conducted. As such, because the pen tip is not advanced or retracted at the moment that the writing instrument is expanded or contracted, there is a disadvantage in that the pen tip is not rapidly advanced or retracted.
As well, in the conventional pen tip advancing and retracting device of the writing instrument, because the main body, having a relatively small diameter, is inserted into the cap body, having a relatively large diameter, the balance and harmony, which are related to aesthetic principles of form, are deteriorated, thus reducing the aesthetic value.
Moreover, the conventional pen tip advancing and retracting device of the writing instrument is inconvenient because the operation of expanding or contracting the main body and the cap body is independent from the operation of advancing or retracting the pen tip.